1. Technical Field
The present invention relates to a double sided simultaneous grinding method for plate-like workpieces such as a semiconductor wafer or a quartz substrate for an exposure original, a double side simultaneous grinding machine, a double side simultaneous lapping method, and a double side simultaneous lapping machine.
2. Background Art
Surface grinding has been used conventionally in precision processing of plate-like workpieces such as semiconductor wafers or quartz substrates. Surface grinding has come to be used instead of lapping, or the like, because the grinding rate is high, a wafer having high flatness is easily obtained, and so forth.
When a single side surface grinding machine is used in the grinding step, a problem exists that waviness generated in the previous step, i.e., a slicing step, cannot be removed because one side of a wafer is held by a vacuum suction while the other side is ground. In order to solve the problem, a double side simultaneous grinding machine (also referred to as xe2x80x9cdouble head grinding machinexe2x80x9d) has been developed as a technique for simultaneous grinding both sides of a wafer.
Regarding double head grinding methods for simultaneously grinding the surfaces of a wafer, various methods exist. For example, in a creepfeed grinding method, a wafer is passed between a pair of cylindrical grinding stones and thereby ground. In an infeed grinding method, a wafer is ground using a pair of cup-type grinding stones such that the grinding stones pass along the center of the wafer with the grinding stones and the wafer rotating together.
An infeed-type double side simultaneous grinding machine 1a used for grinding a semiconductor wafer, illustrated in FIG. 6, comprises a pair of cup-type grinding stones 20, 21 that rotate in the same direction, two pairs of plate-like workpiece press rollers 4 for supporting a plate-like workpiece W on each side, four plate-like workpiece guide rollers 5 for supporting a circumference of the plate-like workpiece W, and a pair of plate-like workpiece driving-holding rollers 3 for rotating the plate-like workpiece W in an opposite direction to the direction of the grinding stones and holding the workpiece. The cup type grinding stones 20, 21 consist of a cup-shaped stock 2a, a grinding stone portion 2b and a grinding stone rotating shaft 2c. Grinding stone segments (not shown) are connected to a grinding surface of the grinding stone portion 2b. The plate-like workpiece W and the cup type grinding stones 20, 21 are rotated at a predetermined rotational speed. Grinding fluid is generally fed from a central hole (not shown) of the grinding stone rotating shaft 2c, or poured onto outer periphery or an inside portion of the grinding stone.
Along with the development of the double side simultaneous grinding machine, a double side simultaneous lapping machine for single wafer processing has been developed in place of conventional batch processing lapping machines which have low accuracy and low productivity. The lapping process using this single wafer processing lapping machine has the advantages of the surface grinding, such as high efficiency in processing and automation with high accuracy. Further, this lapping process has the advantages of conventional lapping, obtaining the same surface condition and an equal back surface condition.
A double side simultaneous lapping machine of the infeed-type 1a is shown in FIG. 6. The pair of cup-type grinding stones 20, 21 is replaced with flat lapping turn tables. For driving a plate-like workpiece, the lapping machine adopts the same mechanism as that of the double side simultaneous grinding machine. However, there is a wide variance in terms of feeding the grinding stones or the turn tables. Feeding the grinding stones in the grinding machine is accomplished by controlling a servomotor or the like, which is a so-called xe2x80x9cinfeedxe2x80x9d. On the other hand, since the turn tables of the lapping machine are basically controlled at a constant pressure, the turn tables are always supported by a pressurizing mechanism such as air cylinder.
As to a difference in actual processing of the plate-like workpiece, the material operating in the grinding machine is bonded abrasives of the cup type grinding stones, while the lapping machine uses a lapping fluid (slurry) containing alumina abrasives and the like which are loose abrasives.
In recent years, the above-mentioned infeed-type grinding method has been used generally because of the advantage of easily obtaining high flatness as compared to the creep-feed type. However, in the infeed-type method, a problem exists that warpage (hereinafter also referred to as xe2x80x9cwarpxe2x80x9d) is apt to be generated in the ground workpiece due to an unbalance of cutting loads on each side, and so forth.
A technique is known wherein coolant is injected from static pressure pads such that a plate-like workpiece is stably supported (for example, see Japanese Patent Laid-open Publication (Kokai) No. 9-262747). However, it has been found that this technique necessarily cannot sufficiently suppress the generation of warpage. Moreover, it has been found that the warpage of the wafer after double head grinding is apt to be worse (degrade) than the warpage before the grinding. Since it is difficult to remove warpage in processing steps subsequent to the grinding step, such problems should be solved in the grinding step to achieve a higher flatness.
The present invention has been accomplished in view of the above-mentioned problems, and its major object is to provide a double side simultaneous grinding method using a double side simultaneous grinding machine wherein the generation of warpage of a plate-like workpiece is suppressed and or the degradation of warpage generated in a previous step is prevented. Thereby the plate-like workpiece can be processed to have high flatness on both sides. An object of the present invention is also to provide a double side simultaneous grinding machine having such characteristics.
Another object is to provide a double side simultaneous grinding method, wherein a plate-like workpiece is ground while a degree of warpage is controlled. Thereby, the workpiece can be processed to have a desired warpage. Another object is to provide a double side simultaneous grinding machine having such a characteristic.
A double side simultaneous lapping machine having a similar structure as the double side simultaneous grinding machine has similar problems as those of the double side simultaneous grinding machine described above. Another object of the present invention is to provide a double side simultaneous lapping method, wherein the generation of warpage of a workpiece is suppressed and/or the degradation of warpage generated in a previous step is prevented. Thereby, the workpiece can be lapped to have high flatness on both sides. Another object is to provide a lapping method wherein the workpiece is lapped while a degree of warpage is controlled. Thereby, the workpiece can be processed to have a desired warpage. Another object is to provide a double side simultaneous lapping machine having such characteristics.
In order to solve the aforementioned problems, the present invention provides a method for simultaneously grinding both a front surface and a back surface of a plate-like workpiece that is held and simultaneously ground on both sides using a pair of grinding stones opposed at both sides of the workpiece, wherein a relative position of at least one of a center between stone surfaces of the pair of grinding stones and at least one of a center of thickness of the plate-like workpiece and a center of the holding means for holding the workpiece is controlled while performing the grinding.
The center of thickness of a plate-like workpiece is a reference for defining a position of the plate-like workpiece and may be, for example, a line or plane passing points (center) of one half of the thickness at two or more points on a surface of the plate-like workpiece.
The center of holding means for holding the plate-like workpiece, for example when the plate-like workpiece is supported on both a front surface and a back surface of the workpiece, is a virtual plane or line passing points one half of the distance between the pair of holding means provided at each side of the workpiece, namely a plane approximately parallel to the plane passing the center of thickness of the plate-like workpiece.
If the plate-like workpiece has high flatness (parallelism), the center of the holding means for holding the plate-like workpiece coincides with the center of thickness of the plate-like workpiece. That is, the center of the holding means for holding the plate-like workpiece indirectly reflects the center of thickness of the plate-like workpiece, i.e., the position of the plate-like workpiece.
The center between the stone surfaces of a pair of grinding stones is a reference for defining a position of the grinding stones. In particular, this center may be a virtual line or plane passing points one half of the distance between the pair of grinding stones. More specifically, this center may be a virtual line or plane passing mid-points at two or more points on opposite grinding surfaces, namely a plane or line approximately parallel to the center of thickness of the plate-like workpiece.
That is, in the present invention, the grinding is performed while a relative position is controlled between an arbitrary reference plane or reference line for defining the position of the plate-like workpiece, and an arbitrary reference plane or reference line for defining the position of each grinding stone. More specifically, the position of each grinding surface is always controlled relative to the workpiece. In particular, when the relative position is controlled such that each reference plane of the plate-like workpiece and the grinding surfaces are parallel to each other, control of warpage can be attained with high accuracy.
If, in the method for simultaneously grinding both sides of a plate-like workpiece, the grinding is performed while the relative position between at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece, and the center between stone surfaces of the pair of grinding stones is controlled as mentioned above, the generation of warpage in the grinding step can be prevented and degradation of warpage generated in the previous step can be suppressed, so that whole surfaces of both sides of the plate-like workpiece can be processed to have high flatness. Accordingly, in the grinding step, increased yield and an improvement in productivity can be attained. Therefore, cost can be improved. Further, warpage having an arbitrary degree can be formed intentionally and direction of warpage can be controlled. Thus, the method can be applied to provide characteristics demanded for particular uses of the plate-like workpiece.
In such a case, the grinding can be performed while at least one of the center of thickness of the plate like workpiece and the center of the holding means for holding the plate-like workpiece is always consistent with the center between the stone surfaces of the pair of grinding stones.
If the grinding is performed while at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece is always consistent with the center between the surfaces of the pair of grinding stones as mentioned above, warpage is hardly formed and degradation of warpage generated in the previous step can be suppressed, so that whole surfaces of both sides of the plate-like workpiece can be processed to have high flatness. Accordingly, yield and productivity in the grinding step can be increased, and cost can be improved.
In such a case, the grinding is desirably performed while the difference between at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece, and the center between the surfaces of the pair of grinding stones is controlled so as to be 3 xcexcm or less.
If the grinding is performed while the difference between both centers is controlled so as to be 3 xcexcm or less as mentioned above, the generation of warpage is certainly prevented, so that whole surfaces of both sides of the plate-like workpiece can be processed to have even higher flatness.
Further, in such a case, the grinding can be performed while the difference between at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the work piece, and the center between the surfaces of the pair of grinding stones is controlled so as to be a desired value.
If the grinding is performed while the difference between both centers is controlled so as to be a desired value as mentioned above, a warpage having an arbitrary degree can be formedand/or the direction of warpage can be controlled. Thus, the method can meet specific requirements for the characteristics of the plate-like workpiece.
The present invention also provides a double side simultaneous grinding machine having at least a holding means for holding a plate-like workpiece, a grinding means for simultaneously grinding the both a front surface and a back surface of the workpiece using a pair of grinding stones provided oppositely at both sides of the workpiece, and a controlling means for controlling a relative position of a center between stone surfaces of the pair of grinding stones and at least one of a center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece.
The controlling means for controlling the relative position between at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece, and the center between stone surfaces of the pair of grinding stones is, for example, a means for controlling a position of the line or plane passing points one half of the thickness at two or more points on a surface of the plate-like workpiece and/or the virtual line or plane, parallel to the grinding surfaces, passing points one half of the distance between the pair of holding means when the plate-like workpiece is supported on both the front surface and the back surface of the workpiece, relative to the reference for defining a position of the grinding stones, e.g., the virtual line or plane passing points one half of the distance between the pair of grinding stones, similar to the aforementioned reference for defining the position of the plate-like workpiece.
If the double side simultaneous grinding machine is provided with the controlling means for controlling the relative position as mentioned above, the grinding can be performed while the relative position of both centers is controlled. Thereby, the generation of warpage in the grinding step can be prevented. Therefore, the machine can process the plate-like workpiece to have high flatness for whole surfaces on both sides. Accordingly, if the plate-like workpiece is ground by using this double side simultaneous grinding machine, yield and productivity in the grinding step can be increased. Therefore, cost can be improved. Further, a warpage having an arbitrary degree can be formed and the direction of warpage can be controlled. Thus, the machine can meet requirements for individual characteristics of plate-like workpieces.
In such a case, the double side simultaneous grinding machine is provided with a means for controlling the relative position which comprises a means for detecting a position of the holding means for holding the plate-like workpiece, a means for detecting positions of each grinding stone surface, a computer for processing the detected positions, and a means for changing at least one of the position of the holding means and the positions of the grinding stones based on the detected positions processed by the computer. An actuator, such as a motor, an air cylinder or a hydraulic cylinder, may based as the means for changing the position of the holding means and/or the positions of the grinding stones.
If the machine has such a structure, the position of the holding means for holding the plate-like workpiece and the position of each grinding stone surface are always detected. The detection results are processed by a computer and the position of the holding means and/or the grinding stones is changed based on the data processed by the computer, so that the workpiece is held in a desired position to be ground. Therefore, the machine can process the plate-like workpiece to have high flatness for whole surfaces on both sides. Accordingly, if the plate-like workpiece is ground using this double side simultaneous grinding machine, yield and productivity in the grinding step can be increased, and therefore the cost can be improved.
In such a case, it is desirable that the means for controlling the relative position controls the relative position so as to be 3 xcexcm or less, or to be constant at a predetermined value.
If the grinding is performed using the double side simultaneous grinding machine having the controlling means capable of such control with high accuracy, the machine can process the plate-like workpiece to certainly have high flatness for whole surfaces on both sides.
The present invention also provides a double side simultaneous lapping method in which a plate-like workpiece is held and lapped simultaneously for the both a front surface and a back surface using a pair of lapping turn tables provided oppositely at both sides of the workpiece, wherein a relative position between the center between turn table surfaces of the pair of lapping turn tables and at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece is controlled to perform the lapping.
The definition of the terminology such as the center of thickness of the plate-like workpiece, the center of the holding means for holding the workpiece, the center between turn table surfaces of the pair of lapping turn tables is the same as that discussed with respect to the aforementioned double side simultaneous grinding method.
If, in the method for simultaneously lapping both sides of a plate-like workpiece, the lapping is performed while at least one of the relative position between the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece, and the center between turn table surfaces of the pair of lapping turn tables is controlled as mentioned above, the generation of warpage in the lapping step can be prevented and the degradation of warpage generated in the previous step can be suppressed, so that whole surfaces of both sides of the plate-like workpiece can be processed to have high flatness. Accordingly, yield and productivity in the lapping step can be increased, and therefore the cost can be improved. Further, a warpage having an arbitrary degree can be formed intentionally and the direction of warpage can also be controlled. Thus, the method can be applied to provide characteristics demanded for particular uses of the plate-like workpiece.
In such a case, the lapping can be performed while at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece is always consistent with the center between the turn table surfaces of the pair of lapping turn tables.
If the lapping is performed while at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece is always consistent with the center between the surfaces of the pair of lapping turn tables, warpage is hardly formed and degradation of warpage generated in the previous step can be suppressed, so that whole surfaces of both sides of the plate-like workpiece can be processed to have high flatness. Accordingly, yield and productivity in the lapping step can be increased, and therefore cost can be improved.
In such a case, the lapping is preferably performed while the difference between at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece, and the center between the turn table surfaces of the pair of lapping turn table is controlled so as to be 3 xcexcm or less.
If the lapping is performed while the difference between both centers is controlled so as to be 3 xcexcm or less as mentioned above, the generation of warpage is certainly prevented, so that whole surface of both sides of the plate-like workpiece can be processed to have even higher flatness.
Further, in such a case, the lapping can be performed while the difference between at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece, and the center between the surfaces of the pair of lapping turn tables is controlled so as to be a desired value.
If the lapping is performed while the difference between each center is controlled so as to be a desired value as mentioned above, formation of warpage having an arbitrary degree and control of direction of warpage can be realized. Thus, the method can meet requirements for specific characteristics of the plate-like workpiece.
The present invention also provides a double side simultaneous lapping machine having at least a holding means for holding a plate-like workpiece, a lapping means for simultaneously lapping the both a front surface and a back surface using a pair of lapping turn tables provided oppositely at both sides of the workpiece, and a controlling means for controlling the relative position between the center between turn table surfaces of the pair of lapping turn tables and at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece.
The means for controlling the relative position between at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece, and the center between turn table surfaces of the pair of lapping turn tables, is similar to the reference for defining the position of the plate-like workpiece and previously described above concerning the double side simultaneous grinding machine.
If the double side simultaneous lapping machine is provided with the controlling means for controlling the relative position between at least one of the center of thickness of the plate-like workpiece and the center of the holding means for holding the workpiece, and the center between turn table surfaces of the pair of lapping turn tables as mentioned above, the lapping can be performed while the relative position of both centers is controlled. Thereby, the generation of warpage in the lapping step can be prevented. Therefore, the machine can process the plate-like workpiece to have high flatness for whole surfaces on both sides. Accordingly, if the plate-like workpiece is lapped using this double side simultaneous lapping machine, yield and productivity in the lapping step can be increased, and therefore cost can be improved. Further, a warpage having an arbitrary degree can be formed and the direction of warpage can be controlled. Thus, the machine can meet requirements for individual characteristics of plate-like workpieces.
In such a case, the double side simultaneous lapping machine is provided with a means for controlling the relative position which comprises a means for detecting a position of the holding means for holding the plate-like workpiece, a means for detecting positions of each lapping turn table surface, a computer for processing the detected positions, and a means for changing the position of at least one of the holding means and the lapping turn tables based on the detected positions processed by the computer.
If the machine has such a structure, the position of the holding means for holding the plate-like workpiece and the positions of each lapping turn table surface are always detected, the detected positions are processed by a computer, at least one of the position of the holding means and the position of the lapping turn tables is changed based on the data processed by the computer, so that the workpiece is held in a desired position to be lapped. Therefore, the machine can process the plate-like workpiece to have high flatness for whole surfaces on both sides. Accordingly, if the plate-like workpiece is lapped using this double side simultaneous lapping machine, yield and productivity in the lapping step can be increased, and therefore cost can be improved.
In such a case, it is desirable that the means for controlling the relative position controls the relative position so as to be 3 xcexcm or less, or to be constant at a predetermined value.
If lapping is performed using the double side simultaneous lapping machine having the controlling means capable of such control with high accuracy, the machine can process the plate-like workpiece to certainly have high flatness for whole surfaces on both sides.
According to the present invention, in the double side simultaneous grinding using a double side simultaneous grinding machine, the generation of warpage of a plate-like workpiece is suppressed, degradation of warpage which may be generated due to the grinding is prevented, and the plate-like workpiece can be processed to have high flatness on both sides. Additionally, yield and productivity can be increased and therefore cost can be improved.
Moreover, according to the present invention, the grinding can be performed while a degree of warpage is controlled. Thereby, the workpiece can be processed to have warpage of a desired degree.
Further, according to the present invention, in the double side simultaneous lapping using the double side simultaneous lapping machine, the generation of warpage of the plate-like workpiece is suppressed, degradation of warpage generated in the previous step is prevented, and the plate-like workpiece can be processed to have high flatness on both sides. Additionally, yield and productivity can be increased and therefore cost can be improved.
Moreover, according to the present invention, the lapping can be performed while a degree of warpage is controlled. Thereby, the workpiece can be processed to have warpage of a desired degree.